Yeah I heard they share the same drivers indeed, but the cans are a bit different, and the material certainly looks different, so I'm not sure if they sound the same, and/or if the Creative isolates better than the Denon.

That's quite a bit of a difference in the highs (even though we can't hear nowhere near that anyway...)
Seriously, Denon numbers sound a bit exaggerated to me, but I'm not sure, the difference might come from the different cans/materials.

The CAL! isolate the trebles only, no low frequency isolation at all, so a journey by train will be equally painful as without them. The transducers are the same in the Denons but the Creative's are made of plastic parts only, while the Denons use some metal elements. Both use a crappy wire which is subject to replace for something decent, and then they transform into a great pair of headphones.

I've never heard the aurvana lives, but I have a lot of experience with Creative gear. In my experience, they are a pretty easily comparable to Bose. A "high end" company for the masses. Every set of creative headphones I've heard sounds very colored to me (much like bose). And their better headphones aren't worth the money, especially with sennheiser now covering the low price range

I've never heard the aurvana lives, but I have a lot of experience with Creative gear. ... And their better headphones aren't worth the money, especially with sennheiser now covering the low price range

You are wrong. Creative Aurvana Live! has very good quaility/price ratio.
One of the best alternatives for the portative use

While we're on this, I, as a sometime lurker turned new poster whose been looking for a new pair of likely closed but certainly non-leaky headphones have to ask, how would these two compare with each other and in general in terms of not letting everyone else hear in on my music?

While we're on this, I, as a sometime lurker turned new poster whose been looking for a new pair of likely closed but certainly non-leaky headphones have to ask, how would these two compare with each other and in general in terms of not letting everyone else hear in on my music?

I don't have neither of them, but people say the Denon, at least, doesn't leak too much, so I guess it's fine for you.